. these are elevator bolts, you can get them on line , cheap ( save your money for gas to drive your car ) sand the heads to get them rough,, clean the area well with acetone then epoxy them to were you want then take some acetone again clean the area really really well , ( that fingernail polish remover will work just fine).. then get a pint of fiberglass epoxy its a 2 part system... then but cuts squares out of the fiberglass ' cloth ' not matt.. cut about 4 sheets of cloth to the size that you want then 4 little holes to clear the studs ( cover the studs with those vacumn hose ends ) wet the cloth , slip it over the repair,, massage the both to remove any air pockets.. you will see them,, they look white and compaired to a dark wet look.. once you have the 1 st layer of glass on ( as the layers go one, make each layer 10 mm bigger than the one you just put down, lay the 2nd layer of glass on. massage that into the wet epoxy( add epoxy as needed ),, massage in ,add 3rd layer, , and repete what you did on the 2nd layer add layers untill done,,,, this will make a strong finish
and from now one use antiseize on every bolt that you find.. here's a winter project for you,, remove your front bumper,, clean the threads.. anitseize them put the bumper back one.. just slowly go around your car,, look for any bolt or nut that could use a nice coat of anti seize on the threads